In a manufacturing process of semiconductor devices, various processing apparatuses (semiconductor manufacturing apparatuses) are used for subjecting substrates to be processed, such as semiconductor wafers (hereinafter referred to as “wafers”) to processes such as oxidation processes, diffusion processes, and CVD (Chemical Vapor Deposition) processes. As one of these apparatuses, there has been known a batch-type of vertical thermal processing apparatus, which is capable of thermally processing a number of substrates to be processed at the same time.
The batch-type of vertical thermal processing apparatus includes: a thermal processing furnace; a substrate supporter (also referred to as “boat”) that is loaded to and unloaded from the thermal processing furnace, while supporting a plurality of wafers with predetermined intervals therebetween in a vertical direction; and a transfer mechanism configured to transfer a plurality of wafers between the boat and a container (also referred to as FOUP) capable of containing a plurality of wafers with predetermined intervals therebetween. The transfer mechanism includes: a base table capable of being elevated, lowered, and rotated; and a plurality of transfer plates (also referred to as “forks”) for supporting wafers, the transfer plates being disposed on the base table such that the transfer plates can be moved forward and rearward.
As methods for transferring the plurality of wafers by the transfer mechanism, there are a soft landing method (method for softly transferring the plurality of wafers) which does not have an aligning (positioning) function, and an edge grip method (method for accurately and promptly transferring the plurality of wafers while gripping an edge of each wafer) which has an aligning function.
As a boat, there has been known, in addition to a type of boat in which the plurality of wafers are respectively supported by a plurality of grooves or projections that are formed on a plurality of support columns, another type of boat in which the plurality of wafers are respectively supported on a plurality of annular plates (ring plates) having a diameter larger than that of the wafer via a plurality of substrate support pieces (see, JP4-133417A, for example). According to the latter type of boat, a desired film can be formed on each wafer without being influenced by the support columns, whereby an in-plane uniformity of the film thickness can be improved. In addition, a transfer operation of the transfer mechanism can be facilitated and accelerated.
FIG. 10A is a schematic side view of a conventional fork. FIG. 10B is a schematic side view of the conventional fork 50 in a state wherein a distal portion thereof is bent. As shown in FIGS. 10A and 10B, a regulation part 51 of about 0.8 mm in height for regulating a peripheral portion of a wafer w is disposed on an upper side of the fork 50 at a position thereof corresponding to the peripheral portion of a wafer w. In addition, the fork 50 is provided with a step or a recess 52 of about 0.5 to 1 mm in height at an area to be overlapped by the wafer w excluding the peripheral portion thereof, in order that, even when the fork 50 and/or the wafer w are bent, the fork 50 and the wafer w are not brought into undesired contact with each other. Because of this shape, a total thickness t of the fork 50 is as large as about 3 mm. When the load (weight) of a wafer is applied to the distal portion of the fork 50 having such a shape, the fork 50 is bent with a relatively large bending amount.
As described above, in the conventional vertical thermal processing apparatus, the thickness of each fork of the transfer mechanism is large, and the bending amount thereof is also large. Thus, it is difficult to transfer a plurality of wafers to a boat of narrow pitches. In particular, when a ring boat is used, only a limited number of wafers can be transferred, i.e., the number of wafers to be processed is undesirably limited (the uppermost limit is at most about 75 wafers).